The regularity of reproductive cycles in all species depends upon the sequential waxing and waning of progesterone secretion by the corpus luteum. Thus, by understanding the hormonal control of luteal function one gains the capability of regulating reproductive potential either by inhibiting luteal function for contraceptive purposes or by sustaining inadequate luteal function to overcome one form of human infertility. In this study, the rabbit will be used as an experimental model. Estradiol is the principle luteotropic hormone in this species and is thought to interact with the corpus luteum through receptor mediation. The rabbit corpus luteum is also thought to be influenced by an LH-linked adenylyl cyclase and by prostaglandins. However, it is unknown whether LH and prostaglandins have a direct effect on the corpus luteum or whether the effect of these hormones can be explained by changes in the level of estrogen receptor. Thus, the purpose of this proposal is to understand the interaction between estradiol, LH, and prostaglandins and to determine the relative importance of estrogen receptor and LH-stimulated adenylyl cyclase to luteal function in the rabbit. Experiments are designed to determine 1) whether the physiological variations in the level of estrogen receptor during luteal life can be explained by the known interaction between estradiol and progesterone in regulating the estrogen receptor, 2) whether an LH-linked adenylyl cyclase system has a direct influence on luteal progesterone secretion which is independent of estrogen receptor, 3) whether prostaglandins play a physiological role in luteolysis through interference with either LH receptor or estrogen receptor, and 4) whether prolactin mediates the effect of estradiol in preventing luteal regression in hysterectomized rabbits.